This invention relates to a device for measuring a respired amount of air having an impedance pneumograph, and more particularly to a device for measuring a respired amount of air capable of automatically calibrating a measuring signal produced from the impedance pneumograph and indicating an amount of air respired.
An impedance pneumograph is a device for detecting by using a pair of electrodes fitted to the breast of a living body, for example a patient the variation in the amount of air respired by the patient from the variation of the impedance between the electrodes occurring in accordance with the patient's respiration. Accordingly, in the case of measuring a respired amount of air by (a respired amount of air-measuring device having) an impedance pneumograph, it is necessary to first calibrate the output signal of the impedance pneumograph in accordance with the respired amount of air. Conventionally, this calibrating operation was manually carried out. That is, the calibrating operation of the device was performed by manually increasing or decreasing the amplitude of the output signal of the impedance pneumograph using as a reference the output signal of a respired amount of air-gauging instrument such as a hot wire anemometer capable of gauging the absolute value of the respired amount of air. Such manual calibrating operation, however, is complicated and requires much time. Since, during the calibrating operation, a sensing section of the hot wire anemometer is usually set in the patient's mouth, the prolongation of the calibrating time causes a higher load to be applied to the patient. Actually, since this type of device is operated by a doctor or nurse who is unfamiliar with the handling operation, very much time is required for calibration, which will extremely distress the patient. This type of device, therefore, has low practicability.